The zoeae are actually a lot smaller than they appear to be in the video. With the naked eye, it’s hard to tell them apart from the bubbles circulating in the tank. They can easily be mistaken for bubbles or tiny bits of debris. However, their uniform size and tiny tails give them away.
In a comment yesterday, jhamkins asked a really good question about the strong currents in the tank that are caused by the exhaust from the undergravel filter. Does the current negatively impact the shrimp?
The literature generally recommends a calm environment with as little agitation as possible to simulate conditions in natural anchialine pools. However, from what I’ve observed in videos posted by hobbyists and entrepreneurs who are successfully breeding opae’ula in tanks, relatively strong current doesn’t seem to be a problem.
The agitation from sponge filters is apparently a lot more subdued than undergravel filters, so they may be a better bet for breeding. However, the colony in my 10-gallon with an undergravel system seems to be breeding rapidly. The juveniles outnumber the adults, and the ratio in just a few weeks seems to have climbed to 2 to 1. On the other hand, the colonies in the two tanks with sponge filters have yet to breed. However, other factors besides filters may be the problem.
This video gives you a close-up of the turbulence from the exhaust, and as you can see, it doesn’t seem to bother the shrimp. In fact, they seem to congregate in the vicinity of the exhaust at both ends of the tank. I included frames of shrimp on the coral mound very close to the exhaust, and they obviously don’t seem to bothered.
Still, the sight of zoeae being tossed around by the current could be unnerving. My guess is that opae’ula are robust even as larvae and aren’t affected by currents as long as they have access to a wide range of zones where the currents are relatively weak.
I keep the filters in all my tanks running 24/7.
I’m by no means convinced that strong currents aren’t a problem, but in my experience, the levels in my tanks appear to be safe.
Btw, in the video, the current and agitation appear to be a lot stronger than it really is. The exhaust from the undergravel filters emerges as a stream of tiny bubbles, so the impact on the water doesn’t appear to be as harsh. The benefits, however, of the constant flow of oxygen are obvious.